1. Field
The field of the invention is endless track assemblies for snow grooming vehicles, and more particularly the endless belts used in such assemblies.
2. State of the Art
Snow groomer vehicles use endless tracks having elongate flexible plastic belts made endless by connecting their ends with lacing or the like. The belts are typically reinforced by plies of fabric incorporated into the rubber-like belt material. Steel cleats are bolted across the belt at intervals of a few inches therealong. Each belt is engaged by a power transmitting sprocket wheel, which forces the belt to travel around a set of guiding wheels called bogies. The powered belt imparts horizontal shear force to the cleats, which engage the snow to propel the vehicle. Much development has gone into the design of the elongate cleat members, with the object of providing maximum traction and resistance to side slipping of the vehicle. Typical cleat constructions are disclosed in U.S. Pat. Nos. 3,765,731, 4,560,211, 4,281,882 and 4,059,315. Typically the ground contacting cleat, also called a grouser, is fastened to the outside of the flexible belting by bolts or rivets installed in matching holes in the cleat, belt, and a metal backing plate on the inside of the belt. The shanks of the bolts bear against the side of the holes in the belt to transfer the shearing forces to the cleats, perhaps initially aided by friction between the belt and the cleat and backing plate. The belt material is malleable, and the fabric plies are discontinuous at the holes, so that none of the remaining fabric plies or strands are positioned to resist elongation of the holes and concentrated stresses. The holes therefore become permanently elongated, which loosens the cleats upon the belt.
The fabric incorporated into the structure of state of the art flexible belts typically provides warp and woof strands, the warp being lengthwise to the belt and the woof being crosswise. The longitudinal warp fibers are intended to give the belt tensile strength in the direction of its length and the warp fibers to provide dimensional stability, and to prevent lateral disintegration or stretching of the belt in that direction. This relationship between the reinforcing fibers or cord is to a large degree responsible for the lack of elongation resistance in the cleat mounting holes, since the warp fibers are capable of only stress resistance in the longitudinal direction of the belt. Being cut at the holes in the belt in that particular location at each cleat mounting hole, there is no elongation resistance other than a very small amount provided by the malleable, rubber-like, belt material. The hole deformation and elongation occurs even with great clamping force between the cleat and the backing plate. This is because the belting material creeps under prolonged stress to relieve the clamping force, substantially eliminating the initially helpful friction between the belt and the cleats and the backing plate. The use of increased numbers of holes and bolts, as indicated for example in U.S. Pat. No. 4,281,882, FIG. 8, helps somewhat. However, this approach produces a correspondingly weakened belt, and is therefore self-limiting, and it has not proven satisfactory. In U.S. Pat. No. 5,033,801, a more effective approach to limiting hole elongation is disclosed. The aforesaid backing plate is provided with beltward projections which impress themselves into the fabric of the belt without rupture of the associated strands of fabric, to resist a large portion of the shearing force, relieving the stress upon the holes through the belt. Similar projections are applied to a belt contacting portion of the grouser extending upwardly to embed into the outside of the belt. See FIG. 8. In accordance with a variation of this approach, existing cleat and backing plate assemblies may be supplemented by a gripping plate interposed between the existing grouser and the belt, carrying the aforesaid projections. See FIG. 12. These approaches to the hole elongation problem have proven significantly successful, although not completely elimininating the problem. Also, they require additional expense and design effort to be directed into the grouser, the backing plate and any interposed gripper plates. An improved endless track assembly, including an improved belt design itself more resistant to hole elongation, is needed.